The invention concerns an electrophotographic print or copy device in which a toner application unit applies electrically charged toner particles to the surface of a first carrier element. At least one part of the applied toner particles is transferred from the first carrier element to a second carrier element. A cleaning unit removes remaining toner particles from the first carrier element. A further aspect of the invention concerns a device to clean a roller of toner particles in an electrophotographic printer or copier, on whose surface is conveyed a particle mixture made up of electrically charged toner particles and ferromagnetic carrier particles. Furthermore, methods to operate an electrophotographic printer or copier and to clean a roller in an electrophotographic printer or copier are specified.
In electrophotographic printers or copiers, image development methods are used that develop electrostatic charge images on surfaces (for example, charge images on a photoconductor) over an air gap or in direct contact with triboelectrically charged toner that is located on a surface of an applicator element. Such an applicator element can, for example, be implemented as a roller or as a continuous band. The toner particles are triboelectrically charged before the transfer to the applicator element. In known printers or copiers, a two-component mixture made of toner particles and ferromagnetic carrier particles is generated. The two-component mixture is mixed in the printer or copier such that the toner particles rub on the carrier particles, whereby they are triboelectrically charged.
It is known to ink surfaces with toner particles that are comprised in a two-component mixture. A magnetic roller arrangement transports the two-component mixture in an area with slight separation between the magnetic roller arrangement and the surface to be inked, whereby a magnetic field of a magnet element acts on the two-component mixture. In this area, a magnetic brush is fashioned that comprises carrier particles and toner particles, whereby only the latter is transferred to the surface to be inked. The carrier particles are held back due to the magnetic field.
In other known printers or copiers, the transfer of the toner particles from the magnetic roller arrangement to the applicator element ensues over an air gap between the magnetic roller and the applicator element that is not completely bridged by the accumulation of the two-component mixture. The transfer of the toner particles to the applicator element surface can be supported by an auxiliary transfer voltage, meaning by a potential different between magnetic roller and applicator element.
During an image development event, the toner is transferred via an air gap or via direct contact from the applicator element surface to the surface bearing a charge image (for example, to the surface of a photoconductor drum or a photoconductor band), corresponding to a charge distribution of a latent charge image. Corresponding to the latent charge image, toner particles remain on the surface of the applicator element in the form of an image negative of the developed charge image. The toner particles remaining on the applicator element must be removed from the applicator element before a new application of a closed homogenous toner layer on the applicator element. The unprinted surface of a print page with text is approximately 95% of the total surface. Given printing of such an average print page, approximately 95% of the toner particle quantity applied to the applicator element must thus be removed from it. Depending on the type of print image to be inked, 0 to 100% of the toner particle quantity must be removed from the applicator element.
In print systems with high print speed, the cleaning of the applicator element only insufficiently ensues with the aid of known cleaning devices. After multiple applications of toner particles on the applicator element, and after incomplete cleaning of the toner particles remaining on the applicator element after the inking of the latent charge image, these form a non-uniform thick layer on the applicator element. The inhomogeneous toner layer of different thickness can cause print image interferences, such as “memory effect”. Given memory effect, the preceding print image is visible in inked regions of the print image as a result of the inhomogeneous toner layer on the applicator element that is transferred as a print image onto a medium to be printed. For a qualitatively high-grade print, a complete removal of the remaining toner particles is therefore necessary before the new application of toner onto the applicator element.
If, given a photoconductor drum, the latent charge image is developed, meaning inked with toner particles corresponding to the charge distribution, and the toner image is transfer printed onto a carrier material, some residue of the toner image remains on the surface of the photoconductor drum. This toner residue must be removed from this before the new application of a latent charge image on the photoconductor drum.
It is likewise necessary in print or copy devices to remove toner particles from photoconductor bands, transfer bands and magnetic rollers in order to not affect the electrophotographic process and to ensure a high print quality.
In known print or copy devices, the cleaning (meaning the removal of toner residues) of photoconductor drums ensues with the aid of plastic brushes that have direct contact with the surface of the photoconductor drum. Wear thereby ensues both on the plastic brushes themselves and on the photoconductor drum. Furthermore, the toner particles to be removed are subject to a significant mechanical stress during the cleaning process with such brushes, whereby the physical properties of the toner particles are negatively changed.
From U.S. Pat. No. 4,383,497, an arrangement for cleaning an applicator element is known in which the toner particles are mechanically stripped from the applicator element with the aid of a stripping blade that is in direct contact with the surface of the applicator element. The toner particles are thereby mechanically significantly stressed, meaning high mechanical pressure and shear forces are exerted on the toner particles. The mechanical stress of the toner particles leads to a negative change of the physical properties, or even to a loss of functionality of the toner material, whereby print image interferences can ensue given a reuse of these toner particles to develop subsequent print images. Such blades are, for example, produced from plastic, metal or from metal coated with ceramic. The direct contact between blade and applicator element above all effects a high wear in the blade. The wear is different in regions of the blade, whereby a non-uniform cleaning of the structure element ensues given a worn blade. This blade must be exchanged frequently in high-capacity printing systems. Moreover, the surface of the applicator element can be damaged by the mechanical friction between blade and applicator element. Such damage can altogether impair the function of the applicator element.
From German Patent Document DE 41 05 261 A1, an image generation device with two identical image generation units is known. A first image generation unit is arranged in a development position and operates as a development unit. The second image generation unit is arranged in a cleaning position and operates as a cleaning unit. The image generation units are alternatively and repeatedly brought into the development position and the cleaning position. The particle mixture comprised in an image generation device is thereby used for application of toner material and, at another point in time, for cleaning.
From U.S. Pat. No. 4,141,165, an electrostatic copier is known in which magnetic brushes are used to ink a charge image of a photoconductor drum and to remove residual toner from the photoconductor drum. A roller that internally comprises stationary magnets is used for application and cleaning. The magnetic brushes are generated with the aid of the magnets. A particle mixture is removed from the surface of the roller with the aid of scrapers whose edges scrape on the surface of the roller.
A magnetic brush cleaning device for a copy device is known from German Patent Document DE 32 46 940 A1. With the aid of a magnetic brush device, it is achieved that a mixture made of a magnetic carrier and the toner glides over the surface of a photoconductor and absorbs toner residue adhering to the photoconductor surface. The cleaned toner is supplied with the aid of a toner recovery device that comprises a plurality of rollers. Toner material adhering to the rollers of the toner recovery device is removed from these with the aid of scrapers scraping on the rollers.
From German Patent Document DE 32 41 819 C2, a magnetic brush cleaning device is known in which a cleaning roller is provided in which internal stationary magnets are provided that generate magnetic brushes. The magnetic brushes slip over the surface of a photoconductor drum and clean off residual toner from it that remains after the transfer printing of a toner image on the control device. The cleaned-off toner material is transferred from the magnetic roller to a second roller. With the aid of a stripper that lies on the surface of the second roller, the toner material is scraped from the surface of the second roller.
From Japanese Patent Document JP 2000267397 A, magnetic rollers are known that are used to ink a charge image of a photoconductor drum and to clean off residual toner from the photoconductor drum. Two abutting magnet elements that are arranged opposite the surface of the photoconductor drum prevent the contact of the magnetic brushes with the surface of the photoconductor drum. The magnets of the magnetic roller rotate with the magnetic roller.
From German Patent Document DE 32 49 767, a cleaning device is known for the removal of developer particles from an imaging surface of a moving, photoconductive band in an electrophotographic copier device. The back side of the band is also cleaned of possible toner residues and dust deposits with the aid of this cleaning device. The band is pressed against a cleaning roller with the aid of a stripper. Via magnets arranged in the cleaning roller, the stripper is pressed against the cleaning roller by means of a plate made from a magnetizable material.
From German Patent Document DE 39 40 079 C2, a method is known to remove a thin layer from a movable photoconductive part of an image generation device. Toner material that is located on a roller surface is thereby removed with the aid of a stripper that scrapes the toner material from the roller surface.